TECHNOLOGY SiC POWER ELECTRONICS
test-element-group characterisation tool indicates that the contact resistivity of the anode contact is approximately 4–5 mΩ cm2
. This indicates that
further improvements in on-resistance could result from increasing the acceptor concentration in the anode’s top layer and optimising the process.
One of our next goals is to eliminate basal-plane dislocations in SiC. These imperfections, which lead to carrier-recombination-induced dislocation glide that can in turn create Shockley-type stacking faults, degrade device performance: on-resistance and leakage current both increase. In our latest devices, the device area is typically just 2–3 mm in diameter, including the termination region. But if this class of device is to be considered for electric power infrastructure, its area will need to increase to more than 1 cm2
,
so that it can handle currents far greater than 100 A. The density of basal-plane dislocations in our latest SiC epitaxial layers is in the 0.1–3 cm-2 range, and this must be plummet to below 0.01 cm-2
to enable high-yield production of devices with high current-handling capabilities.
Another target is the development of 20 kV-class power-switching devices, such as thyristors, IGBTs, and bipolar junction transistors (BJTs). We have started with a preliminary study on UHV BJTs, demonstrating a 21 kV BJT with a current gain of 63. Now we will try to improve the performance of these devices, while undertaking trials to fabricate other types of UHV power switching device.
The author would like to acknowledge J. Suda, H. Miyake, H. Niwa, T. Okuda, N. Kaji, and S. Ichikawa from Kyoto University for their contributions to this study.
© 2014 Angel Business Communications. Permission required.
Figure 8. Device simulations enabled optimisation of the junction termination structure, which was improved by understanding the electric fi eld strength distribution near the edge of a pin diode under high-voltage (18 kV) reverse bias. The original structure with its multiple space-modulated rings offers reduced electric fi eld crowding near the edge
Figure 9. A fabricated diode during high-voltage testing
Figure
10.Current density-voltage characteristics of a mesa SiC pin diode with a space-modulated JTE structure (total JTE length of 1050 mm). The voltage- blocking layer is 260 μm-thick and doped to a density of 1×1014
cm-3 . At a reverse voltage of 26.9 kV
(the limit of our measurement set-up), this diode did not exhibit breakdown
Further reading Jun Wang et. al. IEEE Industrial Electronics Magazine, June, 16 (2009) Shuhei Ichikawa et. al. Appl. Phys. Express 5 101301 (2012) Hiroki Niwa et. al. Appl. Phys. Express 5 064001 (2012) Hiroki Miyake et. al. IEEE Electron Device Lett. 33 1598 (2012) Naoki Kaji et. al. Ext. Abstr. Int. Conf. on Silicon Carbide and Related Materials 2013, p.86. Lin Cheng et. al. Ext. Abstr. Int. Conf. on Silicon Carbide and Related Materials 2013, p.85.
March 2014
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